Mixed-valence magnetism in TiO2/TiOx superlattices
Abstract
Epitaxial TiO2 and TiOx superlattices, ~ 1-nm thick per layer by sputtering at 570°C using pure argon on sapphire substrates. From HR-TEM, the periodically alternating layers are well-defined. XPS analyses based on the binding energy of Ti 2p3/2 peaks suggest the co-existence of Ti+3 and Ti+4, thus verifying the mixed-valence nature. The M(H) curves measured at room temperature using SQUID showed hysteretic loops typical of ferromagnetism. Electrical transport measurements were done at zero field demonstrate transition of charge ordering at low temperatures, reminiscent of what was found in Ti-rich Ti1+xO2 single-layer thin films, made by Ti ion implantation into TiO2 crystals, in which randomly distributed TiO2, Ti2O3 and TiO were found to coexist. Preliminary First-principle (ab initio) calculations to understand the roles of oxygen vacancies in various TiO2 super-cells could indeed lead to spontaneous magnetizations. We thus argue that mixed-valence titanium ions are responsible for the magnetism
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2015
- Bibcode:
- 2015APS..MARA13013H